Organic polymeric materials such as plastics, rubber and resins, and synthetic, lubricating and mineral oils are subject to thermal, oxidative and photo-degradation. A great variety of stabilizers are known in the art for stabilizing a diversity of substrates. Their effectiveness varies depending upon the causes of degradation and the substrate stabilized. In general, it is difficult to predict which stabilizer will be most effective and most economical for any one area of application. For example, stabilizer effectiveness in reducing volatility may depend upon preventing bond scission in the substrate molecule. Limiting embrittlement and retaining elasticity in a polymer or rubber may require prevention of excessive crosslinking and/or chain scission. Prevention of discoloration may require inhibiting reactions which yield new chromophores or color bodies in the substrate or stabilizer. Problems of process stability and incompatibility must also be considered. These and other undesirable degradative effects may originate as a result of thermal degradation, oxidation, photodegradation or some combination of these processes with the organic materials under conditions which are not well understood.
It has now been determined that the compounds of this invention possess an unusual combination of desirable properties which makes them particularly effective and useful as stabilizers. The compounds are particularly effective in protecting polyolefins, high impact polystyrene, rubbers such as polybutadiene and styrene-butadiene rubber, and other elastomers wherein retention of elasticity and inhibition of crosslinking, crazing, discoloration, odor formation and exudation are basic requirements.
Some of the hydroxyphenylthio compounds found useful in stabilizing organic substates are known.
A related series of U.S. Pat. Nos. 3,576,883; 3,786,100; 3,897,500 and 3,956,359 disclose keto substituted alkylidenedithiobisphenols wherein bis(3,4-di-tert-butyl-4-hydrophenyl) groups and various alkylidene bridging groups are present. In all cases a methyl substituent must appear on the alkylidene linking member of these compounds. The compounds of these patents are found useful for reducing blood cholesterol levels in warm-blooded animals and no mention or suggestion of their possible use as stabilizers is made.
M. B. Neuworth et al., J. Medicinal Chemistry, 13, 722 (1970) describes the same compounds as disclosed in the four patents mentioned supra as well as a number of comparable alkylidenedithiophenols having a variety of substituent groups on the phenyl ring and on the linking alkylidene member. Again, the only utility given for said compounds is for hypocholesterolemic activity in warm-blooded animals.
Three Japanese Kokai Nos. 79/163,536; 80/9,041 and 80/17,316 (CA, 93, 71280x (1980); CA, 93, 94980q (1980) and CA, 93, 149970u (1980) respectively) describe 2,2-bis(3,5-di-tert-butyl-4-hydroxyphenylthio)propane as a hypocholesterolemic agent.
U.S. Pat. No. 3,704,327 discloses bis(3-methyl-5-tert-butyl-4 hydroxyphenylthio)methane and 1,1-bis(3-methyl-5-tert-butyl-4-hydroxyphenylthio)ethane as antioxidants for rubber. The instant compounds differ structurally from these prior art compounds by being substituted on the phenyl ring by two tert-butyl groups ortho to the hydroxy in each ring and by having the alkylidene linking member substituted by a total of at least five carbon atoms. The instant compounds provide better stabilization performance in a variety of substrates than do the two prior art compounds of U.S. 3,704,327.